International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Upper Cenozoic conglomeratic formations as a rock record of the turning points in the evolution of the Carpathian orogen and its foreland

Published: Apr 2024

Pages: 133 - 154



Abstract: This paper presents the upper Cenozoic post-collisional terrestrial conglomeratic formations of the Eastern and South-Eastern Carpathian foreland subjected to sedimentological and geomorphological analyses including an in-depth review of previous investigations. These formations embrace gravels as the prominent component, together with sands and muds. The unit is up to 190 m thick. The conglomeratic formations are represented by erosional remnants in the Eastern Carpathians, whilst they occur as a continuous body (the Cândeşti Formation) in the South-Eastern Carpathians. The Eastern Carpathian formation ranges in age from the late Serravallian to early Tortonian stages, whilst the Cândeşti Formation extends from the late Early to the late Middle Pleistocene. These formations are separated by 10 Myr, supporting the view the Carpathians and their foreland from North to South evolved diachronously. Their affinity is determined by the sedimentary environment of alluvial fans within the wedge-top depozone of the foreland. This environment arose from simultaneous occurrence of rare intervals of intense floods and presence of highly erodible rocks in fan-supply catchments. Most of the fans are of hyperconcentrated flow-dominated type, whilst part of those within the Eastern ­Carpathians are of debris-flow-dominated type. The fans’ origin was provided by uplifted orogen and stable or subsiding foreland, giving both high gradient and orographic precipitation. The fans accumulated following a time lag after the post-collisional orogen uplift. The facies and architectural differences between the formations are associated with specific sedimentation and regional tectonics. In the Eastern Carpathians thin conglomeratic formation was deposited above the regional angular unconformity by predominant progradation in conditions of the tectonic quiescence and low accommodation space. In the South-Eastern Carpathians the fluvial fine-grained sedimentation gradually passed into the thick conglomeratic Cândeşti Formation during the attenuated subsidence of the Focşani Depression. As the accommodation space decreased, the aggradation of the formation gave way to its progradation.

Keywords: Eastern Carpathians, South-Eastern Carpathians, foreland, upper Cenozoic, conglomerates, alluvial fans

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